Principles of construction and functionality of superconducting power conditioners, as transformers, current conditioners (or so called fault current limiters), are generally known, e.g. from EP 0 345 767 A1 which discloses a superconducting device for current conditioning. The device is based on a quenchable superconductor which is capable to quench from a superconducting state comprising zero resistance to a quenched state comprising a non-zero resistance when the transporting current exceeds a critical value. The device comprises further a metallic member electrically coupled with the quenchable superconductor. The metallic member consists of a resistive element (as a thin metallic layer or multilayer) which is thermally coupled with quenchable superconductor. The device comprises also means for cooling and heat interchange between different parts of the superconducting element and between the superconducting element and a cooler or a cooling medium, and also means for electrical coupling. In operation, the quenchable superconductor is responsible for increase of the impedance of the device at circuit over-currents and due to this to limit fault current to a predetermined level. The task of metallic member, that is according to the EP 0 345 767 A1 shaped as a layer, is to protect the quenchable superconductor against local overheating so called “hot spots”) which may easily destroy the device comprising a slight inhomogeneity of the critical current.
A similar device but with a metallic member which is periodically interrupted in direction of current transport is known from DE 198 56 425 A1. Such metallic member, as a resistive element, may be formed as a layer with a meander shape. The device comprises a perfect thermal coupling of the metallic member with a quenchable superconductor as the main part of superconducting surface stays is direct contact with the metallic member. In test under overcurrents, the device comprises long transient time of quenching (3-5 ms) and long recovery time (typically 800-1500 ms) that corresponds to the time required for returning of the quenchable superconductor at the initial superconducting state after interruption of current transport.
A further superconducting device for current conditioning is known from IEEE Trans. Appl. Supercond. vol. 9, pp. 1365-1368, 1999. The device comprises a quenchable superconductor, a metallic member, means for cooling and heat interchange between different parts of the superconducting element and between the superconducting element and a cooling medium, and means for electrical coupling. The metallic member comprises a resistive element and means for electrical coupling with the quenchable superconductor. The metallic member is electrically and thermally coupled with the quenchable superconductor. Electrical coupling is provided by a plurality in In wires bonded to the quenchable superconductor and a further plurality of In wires jointed to a metallic strip based on a thin Au film. The thermal coupling originates from the means used for electrical coupling (In (indium) wires) in one part, and in other part, through a transverse heat flow in In wired bonded to the Au film and to a substrate (LaAlO3) where the layer of quenchable superconductor is deposited.
A superconducting device for current conditioning known from DE 102 26 393 B4 comprises a quenchable superconductor and a metallic member electrically coupled with the quenchable superconductor. The device comprises further means for electrical coupling and means for cooling of different parts of the device through heat interchange with a cooler or a cooling medium. The metallic member is based on a resistive element made of a resistive foil. The resistive element of the metallic member is thermally coupled with the quenchable superconductor as a substantial part of the heat that is generated in the resistive element is transferred to the superconductor through jointing areas. This happens because the heat in the quenched modus is generated over entire metallic member and, therefore, right nearby to these joints. The resistive foil comprises either a wavy or a “zigzag” shape when it is viewed in plane that is parallel to both the normal to the surface of the quenchable superconductor and the direction of current transport in non-quenched state of the superconductor. In quench and recovery steps, the device comprises medium transient time of quenching (1-3 ms) and long recovery time (typically 200-800 ms).
All of the above-referenced devices aim to condition electrical current in an external circuit which is connected in series to the superconducting device. They may provide the function of a current limiter which results in limitation of the over-currents. However, the prior art devices comprise a reaction time and recovery time (that follow after each quench event) which are too slow for many applications and may be too slow for efficient control of electric power.
It is desirable to further improve the performance of current conditioning devices and to provide a more efficient control of electrical power where much shorter response and recovery times are required in order to not only provide a fast circuit protection but also to provide an desired quick dynamics for such protection as well as reliability of energy supply.
Furthermore, the above-referenced devices comprise an insufficient stability at current overloads which result in inhomogeneous, sometimes in non-reproducible sharing of currents between the quenchable superconductor and the metallic member. Consequently, this causes an insufficient damage threshold at overloads.